Fabrication of flexible organic field effect transistors with high carrier mobility via sheath gas-assisted direct writing Poly(3-hexylthiophene) solution

Flexible organic field-effect transistors (FOFETs) have been receiving wide attention for their high flexibility, tunable electronic behavior, and easy integration with flexible devices, and show extensive application potential in the fields of bendable display, flexible sensing, flexible circuits, etc. The formation process of the active layer in the FOFET greatly affects the device's performance. However, effective crystalline growth manipulation of active materials with high carrier mobility remains challenging, especially for the scalable fabrication process of FOFETs. Herein, a sheath gas-assisted direct writing is proposed for the first time to improve the crystal arrangement of ultrathin poly(3-hexylthiophene) (P3HT) films, realized by a combined effect of rheological shearing and drag shearing from sheath gas flow and substrate movement. A coaxial nozzle is designed with the inner channel for P3HT solution, and the sheath gas goes through the outer channel to assist solution deposition onto the substrate. The inlet gas pressure and the moving speed of the substrate are optimized to achieve higher carrier mobility in the active layer. A prototype FOFET was fabricated with a direct-written thin ionic gel film as the dielectric layer. The resulting carrier mobility reached up to 2.527 ± 1.194 cm2/(V·s), and the operating voltage was less than −1.5 V, the device has bendable capability. The FOFET devices were integrated with a flexible humidity sensor and pressure sensors for health monitoring and ON/OFF switch circuits, demonstrating their functions of signal conversion and amplification. This fabrication technique provides an effective mass manufacturing method for FOFETs, and also can be further adapted for crystallization process control in other materials.